I'd have to dig around in my records for the exact citation, but IIRC, fusion was "get rid of all the system members but one," while fusion was, "combine all the system members into one." So it seemed to be completely different ideas of practice, with integration being "once you absorb all the things keeping you separate, you'll merge."

Fusion seemed to be just "return to singlet, don't care how." It's been a LONG time since that distinction seemed to be a big deal, though.

--Rogan